The invention relates to a driveshaft with two ball type constant velocity fixed joints, a shaft part connecting said two joints, and an axial plunging part arranged in the shaft part.
Driveshafts of said type are predominantly used as sideshafts in the drivelines of motor vehicles. At the input end, they are connected to the differential drive of an axle and, at the output end, to a wheel hub of a driving wheel. The two ball type constant velocity fixed joints are always arranged symmetrically in that the outer joint parts with adjoining journals are located at the outer ends. Said journals can then be easily inserted into the differential drive and into the wheel hub respectively. The convoluted boots for sealing the open annular chambers of the ball type constant velocity joints, which boots require a certain axial length, come to rest on the inside of the shaft, so that the joint centers can move closely to the differential drive on the one hand and to the wheel hub on the other hand, so that large effective shaft lengths between the joint centers of the ball type constant velocity fixed joints can be utilized. In steered front axles, the load spectra differ considerably in respect of the articulation angles because the inner joints in the sideshafts only compensate for compression movements, whereas the outer joints in the sideshafts additionally have to effect steering angles. However, in unsteered rear axles, the load spectra at the inner joints and at the outer joints are approximately the same because in each case, only the compression movements of the wheels have to be compensated for, with the wheel camber remaining substantially unchanged. Regardless of the above, it has been found that the service life values of the joints in the inner and outer sideshafts, and of the inner joints at the differential, vary considerably, with the latter being at a disadvantage.
An example of a ball type constant velocity fixed joint is disclosed in DE-PS-1126199 and an example of an undercut-free joint is disclosed in DE 22 52 827 C3. Other examples of constant velocity fixed joints are shown in DE 25 22670 C2 or DE 2717 936 C3.
It is therefore an object of the invention to provide driveshafts wherein both ball type constant velocity fixed joints, while having substantially identical load spectra, feature very similar service life values while comprising comparable sizes.
The objective is achieved by a driveshaft having two ball type constant velocity fixed joints. The ball type constant velocity fixed joints each comprise: a bell-shaped outer joint part provided with internally positioned first ball tracks; a hub-shaped inner joint part provided with externally positioned second ball tracks and arranged inside the outer joint part; balls engaging pairs of first ball tracks and second ball tracks; and an annular ball cage with circumferentially distributed cage windows in which the balls are held in a common plane. The pairs of first ball tracks and second ball tracks, when viewed in a longitudinal section, form opening angles with to one another for controlling the balls in the ball tracks. In addition, the opening angles of the pairs of first ball tracks and second ball tracks at both ball type constant velocity fixed joints open in the same direction.
It has been found that the relation of the opening angles of the ball hub in the longitudinal section relative to the torque transmitting direction affects the service life of the ball type constant velocity joint, so that the service life values of both ball type constant velocity joints of the driveshaft are adapted to one another if the opening angles at both ball type constant velocity joints correspond to one another. A longer service life is obtained if the direction of opening of the opening angle and the preferred torque transmitting direction are oppositely directed, so that, in accordance with the invention, the shaft has to be mounted in that sense if a preferred torque transmitting direction prevails in the load spectrum, which is of course always the case in the driveline of a motor vehicle.
According to a first preferred embodiment, the bell-shaped outer joint parts extend in the same direction relative to the hub-shaped inner joint parts, with each of the opening angles opening towards the open ends of the bell-shaped outer joint parts.
Both ball type constant velocity fixed joints can be provided in the form of undercut-free joints. One of the joints opens towards the shaft end, so that the shortest possible convoluted boots or rolling boots should be used in order not to shorten the effective shaft length between the joint centers.
According to a second embodiment, relative to the hub-shaped inner joint parts, the bell-shaped outer joint parts are arranged symmetrically relative to one another, especially so as to be positioned towards the outer end of each respective driveshaft, with the opening angle at one of the ball type constant velocity fixed joints opening towards the closed end of the bell-shaped outer joint part.
The attaching journals at the outer joint parts can be integrally formed on to the latter, or an attaching journal can be produced so as to be integral with a base part of an outer joint part, which base part, in the course of production, is welded to an outer annular member of the outer joint part, especially by friction welding. This is particularly advantageous if the opening angles of the tracks open towards the closed end, i.e., the base of the outer joint part. The attaching journals at the inner joint parts or for the inner joint parts are preferably provided in the form of plug-in journals which are form-fittingly and positively connected to the hub-shaped inner joint parts.
Furthermore, according to a preferred embodiment, the inwardly positioned attaching journals of the ball type constant velocity fixed joints are directly welded to an inner journal of the axial plunging element on the one hand and to a sleeve of the axial plunging element on the other hand. In particular, there is provided a convoluted boot which simultaneously extends over and seals the annular opening of one of the ball type constant velocity fixed joints and the annular opening of the plunging element in that one collar of the convoluted boot is positioned on the outer joint part of the ball type constant velocity fixed joint and in that the other collar of the convoluted boot is positioned on the sleeve of the axial plunging element.
The use of shafts in accordance with the invention on the basis of the above mentioned characteristics and features consists in that the ball type constant velocity fixed joints are mounted in such a way that the opening angles open in the direction opposed to the preferred torque transmitting direction.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims and upon reference to the accompanying drawings.
Preferred embodiments of inventive driveshafts will be described below in comparison to a driveshaft according to the state of the art.